Represents a date. The second field reaches 60 only
for leap seconds. The week-day field is 0 for
Sunday, 1 for Monday, etc. The year-day field is
0 for January 1, 1 for January 2, etc.; the
year-day field reaches 365 only in leap years.

The dst? field is #t if the date reflects a
daylight-saving adjustment. The time-zone-offset field
reports the number of seconds east of UTC (GMT) for the current time zone
(e.g., Pacific Standard Time is -28800), including any
daylight-saving adjustment (e.g., Pacific Daylight Time is
-25200). When a date record is generated by
seconds->date with #f as the second argument, then
the dst? and time-zone-offset fields are
#f and 0, respectively.

The date constructor accepts any value for dst?
and converts any non-#f value to #t.

The value produced for the time-zone-offset field tends to be
sensitive to the value of the TZ environment variable,
especially on Unix platforms; consult the system documentation
(usually under tzset) for details.

Like current-inexact-milliseconds, but coerced to a
fixnum (possibly negative). Since the result is a
fixnum, the value increases only over a limited (though
reasonably long) time on a 32-bit platform.

Returns an amount of processor time in fixnum milliseconds that
has been consumed by on the underlying operating system, including
both user and system time.

If scope is #f, the reported time is for all
Racket threads and places.

If scope is a thread, the result is specific to the
time while the thread ran, but it may include time for other
places.

If scope is 'subprocesses, the result is the
sum of process times for known-completed subprocesses (see
Processes)—and known-completed children of the
subprocesses, etc., on Unix and Mac OS—across all places.

The precision of the result is platform-specific, and
since the result is a fixnum, the value increases only over a
limited (though reasonably long) time on a 32-bit platform.

Returns the amount of processor time in fixnum milliseconds
that has been consumed by Racket’s garbage collection so far. This
time is a portion of the time reported by
(current-process-milliseconds), and is similarly limited.

Four values are returned: a list containing the result(s) of applying
proc to the arguments in lst, the number of milliseconds of
CPU time required to obtain this result, the number of “real” milliseconds
required for the result, and the number of milliseconds of CPU time (included
in the first result) spent on garbage collection.

The reliability of the timing numbers depends on the platform. If
multiple Racket threads are running, then the reported time may
include work performed by other threads.

Finds the representation of a date in platform-specific seconds. The
arguments correspond to the fields of the date structure—in
local time by default or UTC if local-time? is
#f. If the platform cannot represent the specified date, an
error is signaled, otherwise an integer is returned.

Converts a date structure (up to 2099 BCE Gregorian) into a Julian
date number. The returned value is not a strict Julian number, but
rather Scaliger’s version, which is off by one for easier
calculations.